In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles. One of the changes involves the complexity of the electrical and drive systems within automobiles, particularly alternative fuel vehicles, such as hybrid, electric, and fuel cell vehicles. Such alternative fuel vehicles typically use an electric motor, perhaps in combination with another actuator, to drive the wheels.
Traditional motor control systems normally include a feedback device or angular position sensor, such as a resolver or encoder, to provide angular frequency (or “speed”) and angular position information about the motor. Feedback devices and associated interface circuits increase the costs of a motor control system, and these costs may become prohibitive in high volume applications such as the production of automobiles. Additionally, an angular position sensor and its associated wiring harness increase the complexity and assembly time of an electric drive system in a vehicle.
Electric vehicles powered by fuel cells, batteries and hybrid systems that include electric motors are becoming more common in the automotive market. As production volumes for electric vehicles increase, the cost of feedback devices and associated interface circuits will become significant. Automakers are therefore always striving to cut costs and reduce the number of parts for a vehicle. The removal of a feedback device for an electric motor control system will lead to significant cost reductions for an electric vehicle.
Hybrid electric and electric vehicles today utilize numerous electric motor control technologies such as the vector control of electric motors. A vector motor control scheme is a computationally intensive motor control scheme that maps the phase voltages/currents of a three-phase motor into a two axis coordinate system. The structure used to excite an electric motor using a vector control scheme is a typical three-phase power source inverter including six power transistors that shape the output voltage to an electric motor. Vector control requires angular position information for the rotor, which is normally obtained via a feedback device or angular position sensor. The objective of the sensorless control is to obtain the rotor angular position information utilizing electromagnetic characteristics of an AC machine, eliminating the angular position sensor and its associated interface circuits.
Methods and systems for sensorless control of an electric motor are described in United States Patent Application Publication Number 2009/0140676 entitled “METHOD AND SYSTEM FOR SENSORLESS CONTROL OF AN ELECTRIC MOTOR,” filed Nov. 29, 2007, which is incorporated by reference herein in its entirety. The methods and systems for sensorless control are applicable to permanent magnet AC machines, such as a 3-phase permanent magnet motor.
Notwithstanding these advances, it is desirable to provide an improved method and system for sensorless control of an electric motor that can be used in conjunction with electric machines including at least permanent-magnet machines, synchronous reluctance machines, and induction machines. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.